In a radio communication network in which interact protocol (IP) set are used (hereinafter, referred to as a “radio IP network” as appropriate), so-called Mobile IP is defined in order to improve the mobility of a radio communication device (refer to Non-Patent Document 1, for example).
In Mobile IP, a care of IP address (Care of Address) dynamically assigned to a radio communication device in accordance with a position of the radio communication device is used.    Non-Patent Document 1: C. Perkins, “IP Mobility Support (RFC2002)” October 1996, IETF.